Today, the United Nations reached a grim milestone, registering 1 million Syrian refugees in Lebanon alone. The Syrian refugee crisis is the worst since the Rwandan genocide 20 years ago, when nearly 1 million people were slaughtered in 100 days.

It began in April 1994 and as that nation prepares to commemorate the dead on this upcoming 20th anniversary, tonight we look at justice after genocide. And remember, just like in Syria, the world watched Rwanda in horror as the bodies piled up. No government did anything to stop it.

But in the 20 years since, Rwanda has undergone a transformation unseen just about anywhere in the world. It's lifted many out of poverty with a staggering 8 percent annual growth rate. It has improved life expectancy, literacy, education and health care. And Rwanda has adopted an official policy of reconciliation.

Much of the credit for that goes to the strong will of President Paul Kagame. But of course he is also criticized for becoming too much of a strong man with increasingly authoritarian ways. We have tackled this often with Kagame himself on this program. And tonight, we focus on peace and reconciliation.

And whether the world actually meant it when they said never again after that terrible genocide, I will ask Rwanda's justice minister.

But first let us just remember.

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AMANPOUR: Oh, the grimaces on their faces. It looks like they died in violent and painful circumstances. Oh, my God. This one still has a rosary around its neck. Yes. He's trying to hide himself. Yes? And the child is trying to shield himself, too.

How many people were killed altogether here?

UNIDENTIFIED MALE (through translator): Thousands. There are 72 rooms full of bodies.

AMANPOUR: Does it still shock you when you see these rooms?

UNIDENTIFIED MALE (through translator): Yes. I still feel bad, especially at night when I can't sleep and I remember when this nightmare turned real and they started shooting us and throwing grenades at all the people crowded in these rooms. I only survived because they thought I was dead.

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AMANPOUR: So how has Rwanda emerged from that nightmare? I asked Justice Minister Busingye Johnston when he joined me earlier from Kigali.

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AMANPOUR: Mr. Minister, welcome to the program and thank you for joining me. Twenty years later, has Rwanda recovered from its nightmare?

BUSINGYE JOHNSTON, RWANDAN MINISTER FOR JUSTICE & ATTORNEY GENERAL: Rwanda has not recovered but it has made very good progress. Twenty years ago, we were a shuttered, unviable region of country from the horror of the genocide. Today we are much better off.

AMANPOUR: I've visited many, many times. But one time particularly just a few years after the genocide, there were 135,000 prisoners in Rwandan jails with a justice system that simply couldn't deal with it. One person told me, at the rate they were going, it would take 200 years to prosecute all the cases.

What is the situation now? Have you prosecuted all the cases of those who were accused of genocide?

JOHNSTON: Thank you for this question, Christiane. Indeed, 130,000 prisoners were in jail waiting to be tried. And this probably was a small number compared to those who were outside also waiting to be tried. The classical court system would not certainly serve this purpose; indeed, in 200 years, we're going to find nobody of us alive.

So what we did was to devise from our own traditional culture and picked up a system called Gacaca. And the Gacaca courts have taken us through 1,958,000 cases in the last 10 years. Right now, we do not have pending genocide cases probably in terms of numbers that we could think about 20, 15 years ago.

Now we have a very small number who are not tried just because of a specific reasons, either waiting for evidence or waiting for something else to happen in their file. But we do not have people waiting on trial because the system cannot deal with them.

AMANPOUR: Mr. Minister, what -- explain to me the genesis of what President Kagame decided, that the justice and the reconciliation and the progress in Rwanda was going to based on reconciliation rather than punishment.

Why was that important? So many people wanted to see punishment of everybody.

JOHNSTON: We had a complex situation in this country. The genocide that happened in this country, neighbors killed neighbors, friends killed friends, husbands killed wives, parents killed children.

Now, if you wanted to have justice where a tooth -- an eye would go for an eye, you would suddenly have to remove very many people's eyes.

So what we thought that was good for our society was also to heal a broken society and try to pick up from where we were, try to build a society.

So the reason why President Kagame and the rest of the leadership of this country decided that justice was going to be based on reconciliation was because, at the end of the justice system, at the end of the handling of all these genocide cases, we needed to build a nation.

We needed a nation that would move; we needed a people in Rwanda that would work together and coexist and continue living side by side in our countryside.

AMANPOUR: Minister Busingye Johnston, thank you very much indeed for joining me.

JOHNSTON: Thank you very much, Christiane.

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AMANPOUR: Now I also asked him to comment on the apologies, the mea culpas that then President Clinton uttered in public and also the pledge that President Obama made in light of what happened in Rwanda.

Here is what those two presidents said.

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BILL CLINTON, FORMER PRESIDENT OF THE UNITED STATES: We must have global vigilance. And never again must we be shy in the face of the evidence.

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BARACK OBAMA, PRESIDENT OF THE UNITED STATES: Too often, the world has failed to prevent the killing of innocents on a massive scale and we are haunted by the atrocities that we did not stop.

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AMANPOUR: So I asked him, what about Rwanda? Is that now safe? And what about Syria where nothing is being done to stop the massacres there?

And the minister told me that they still have to put in place the mechanisms to make sure an eruption of hatred doesn't explode again in Rwanda and of course, he said, that clearly the world has not yet learned those lessons because of what is unfolding under our eyes in Syria right now.

Now back then in Rwanda during the genocide, hundreds of thousands of women were raped during those 100 days. And in the war crimes trials that followed, for the first time ever, rape was enshrined as an act of genocide.

But many of those victims of sexual violence still haven't found justice. And some find it hard to forgive as our Nima Elbagir now reports.

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NIMA ELBAGIR, CNN CORRESPONDENT (voice-over): In the distance, you can just make out two men lashing out. Their victims lie prone. On his knees, one man appears to pray, perhaps for mercy. But none comes. He's struck to the ground and lies unmoving. Nearly 20 years on and this footage is still incredibly hard to watch.

It was filmed during the 100 days of the Rwandan genocide and as the 20th anniversary of the genocide approaches, Rwandans are preparing themselves to commemorate the horror that unfolded in April 1994.

ELBAGIR (voice-over): At the end of the 100 days of the Rwandan genocide, hundreds of thousands of Tutsis and moderate Hutus had been slaughtered by the Hutu majority. And hundreds of thousands of women raped.

At the headquarters of the Association of Women Genocide Survivors in the Rwandan capital, Kigali, women line up every day to receive antiretrovirals, ARVs, to manage their HIV/AIDS. The medications help stave off the worst of the disease -- for now.

Many of these survivors have similar stories to Marijine (ph), passed from attacker to attacker, they contracted the AIDS virus. For them, this is the legacy of the genocide, a legacy Marijine (ph) shares. And as she measures out her daily dose of ARVs, she tells us she believes the rape was a death sentence enacted by her attackers.

MARIJINE (PH) (through translator): There are some in Kigali and Ramagana who very well knew that they were HIV positive. And they deliberately raped people to infect them.

ELBAGIR (voice-over): The Rwandan government has said the 20th anniversary off the genocide is an opportunity to unite in forgiveness. But for Marijine's (ph) daughter, Kileze, that will be hard.

ELBAGIR (voice-over): For Marijine (ph), every anniversary is difficult.

MARIJINE (PH) (through translator): I forgive them because I'm asked by the government to forgive. But the pain is still there.

ELBAGIR (voice-over): It will be another day, she says, when she is reminded of what they've lived through and what they are still struggling to overcome -- Nima Elbagir, CNN.

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AMANPOUR: Such a vivid picture of the trauma that still haunts those victims, despite the reconciliation and despite the progress that we've talked about.

And 11 years after the war in Iraq began, there is trauma still, the soldiers who fought there bear scars that are seen and unseen. For some of those warriors, coming home doesn't stop the screams or end the shooting when soldiers turn on their own brothers in arms as witnessed at U.S. Army Base in Ft. Hood, Texas, when we come back.

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AMANPOUR: Welcome back to the program. It is a sad and shocking statistic that exposes the cost of war beyond the battlefield. Every day, 22 U.S. military veterans take their own lives according to official U.S. figures. That means that one war veteran commits suicide about every hour. And it really does make you think especially that not a single U.S. soldier died last month in war-torn Afghanistan.

On Wednesday, there was another tragedy away from the front line, a U.S. soldier opened fire at the Ft. Hood Army base in Texas, killing three people and injuring 16 others. He then killed himself. According to the Army Secretary, John McHugh, the suspect had served in Iraq, although not in combat operations, and he had also recently seen a psychiatrist.

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JOHN MCHUGH, SECRETARY OF THE ARMY: He was undergoing a variety of treatment and diagnoses for mental health conditions, ranging from depression to anxiety, to some sleep disturbance. He was prescribed a number of drugs to address those.

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AMANPOUR: My next guest is an Iraq war veteran turned U.S. senator and he's so concerned about mental health of soldiers that he's just introduced some new legislation and he joins me now from Capitol Hill.

The first thing I'd like to say is, you know, my thoughts and prayers go out to the families and all the community at Ft. Hood for what happened yesterday. It's a terrible tragedy.

AMANPOUR: And of course, you've been there in terms of having been in the war zone, having returned home.

Is it fair for us to leap to the conclusion, despite what the Army Secretary said, that he potentially had PTSD or mental problems that led to this?

WALSH: Well, Christiane, this issue is very personal to me. I deployed with the first 163rd Infantry Battalion from Montana. I took what I like to say over 700 Montana's finest young men and women with me to Iraq in 2004 and 2005. And when we returned home, one of our soldiers, Corporal Christopher Dana (ph), died by suicide. And so this -- that's why this issue is personal to me. And I want to introduce an act or a bill to solve this problem.

And I would say that in answer, in response to your question, you know, every soldier that deploys, I believe, is going to come home with some type of psychological stress, maybe not a long-term disorder, but it's something that we should be aware of and it's going to react each and every one of our soldiers differently. And our -- each and every service member differently.

AMANPOUR: And the statistics are staggering, Senator. Tell us particularly about the legislation that you've introduced and what you hope it will achieve.

WALSH: Well, the legislation that I introduced, it's the Suicide Prevention for America's Veterans Act. It was brought to me by the Iraq- Afghanistan Veterans for America and what we want to hope -- we hope that this will achieve is it will reduce the number of suicides in our military. And it will focus on the underlying problem of psychological health.

AMANPOUR: Let me put up some of our graphics that you won't see, but our audience will certainly see. I mentioned earlier that some 69 percent of war veterans actually commit suicide at age 50-plus years.

Tell me about how age actually affects this issue.

WALSH: Well, you know, I'm not an expert in this area. But I know that many of the young men and women that served in the Montana National Guard were under the age of 25 and had not been necessarily deployed. So I don't want to say that it's just an issue that's going to affect those that deploy. I think it's an issue that affects all of our men and women who serve in our military and the stresses that they're dealing with on a daily basis. And we have men and women in our -- in the Armed Forces that have deployed two and three times, some have deployed four. So -- and I think it affects each and every one of them differently.

AMANPOUR: Well, as we see here, this other staggering statistic, more than a half a million people, 600,000 people are estimated to likely have traumatic brain injury, PTSD or depression, as you've been saying.

What is the nation? What is the war veterans' association? What is the military doing wrong that these people are not being caught, that there is no safety net for them right now?

WALSH: Well, I don't think we can lay this all on the military. I think that we have to take this on as a society. You know, our men and women that deploy are not with -- necessarily with their fellow service members 24 hours, seven days a week. You know, so we have to rely on family members, community members, to recognize the issues that are being brought up by our service members that have deployed and that -- and when they recognize that there's a problem or something different, that they need to raise the flag so that the military can take action. The military has a tremendous amount of resources, and they've dedicated a tremendous amount of resources to solving this problem. We just have to make sure that the men and women who are suffering are -- we get the resources to those men and women.

AMANPOUR: And yet, of course, the president, Obama, has called this epic suicide situation an epidemic. I mean, and the idea that 22 commit suicide every day is just absolutely -- it's incredible.

What kind of cost would it take to make sure that all those who need it get the kind of help that you're talking about?

WALSH: Well, you know, I don't know what the cost would be as in terms of dollar figures. But in my perspective, this is the cost of going to war, sending our young men and women to -- into combat or into the service that are -- they're willing to give up their lives for this country. And so I believe that this country owes them every opportunity we can to make sure that they're healthy when they leave the service.

AMANPOUR: And when you look around and you see other service people who've come back, you know, some of them may not necessarily have mental issues. But they can't get a job. They can't find employment, many of them are homeless. We see endless sights of men and women who have little cardboard signs, and they're sitting in -- on the sidewalks of major cities, begging, and they're Army veterans, military veterans.

Is there -- you talked about society. Is there something that can be done to make society pony up and pay back the debt to this 1 percent of Americans who fought the wars on behalf of 99 percent?

WALSH: Well, I don't know if there's anything we can make society do. But I think that as service members and now I'm in a position in the United States Senate where I can bring this issue t the forefront to ensure that the Congress understands that we have a problem and make sure that, you know, as we travel around back to our states and our communities, that we let people know that there's a problem and what they can do to help.

AMANPOUR: Senator, thank you so much for joining us on this really important, important subject. We appreciate your time.

WALSH: Thank you, Christiane.

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AMANPOUR: And after a break, justice served in Rwanda, shortly after the genocide, I watched a man who had lost his whole family carefully carry out a very painful task. He told me he did it to honor them and for history.

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AMANPOUR (voice-over): These are the remains of the men, women and children who were slaughtered four years ago. Emanuel Muranduwari (ph) and his colleagues are preserving them as evidence of the genocide that destroyed Rwanda. Emanuel's (ph) afraid that some of these mummified bodies may be what's left of his children. Four of them were murdered at this school along with his wife and another 70,000 people who had come here seeking refuge.

AMANPOUR: How can you work? How can you live with so much death day after day after day? Why do you do this?

EMANUEL MURANDUWARI (PH), RWANDA GENOCIDE SURVIVOR (through translator): I am working here to make this place a memorial. No one here or abroad can deny what happened. They can see the evidence here for themselves.

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AMANPOUR: And all these years later, that evidence is providing victims, very slowly, with justice, even far away from Rwanda, in French courts. And we'll meet a remarkable couple whose marriage is also a mission when we come back.

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AMANPOUR: And finally tonight, we thought we'd end our remembrance of Rwanda not with a body count or a roll call of the lost; how could we, of course? There were 1 million of them. We want to end, though, with an inspiring story of justice delayed but not forgotten.

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AMANPOUR (voice-over): Morning comes to the ancient French city of Reims, the heartbeat of the Champagne district and in whose gothic cathedral 33 kings of France were crowded, including the Dauphin, Charles VII, led to his coronation by none other than France's greatest heroine, Joan of Arc.

Dafroza Gauthier is a modern-day Joan whose morning begins as it has for 13 years, rising at first light to revisit and research a horror some 20 years old and 9,000 kilometers away, and yet whose very name still haunts her life and the conscience of the world: Rwanda.

DAFROZA GAUTHIER, RWANDA RESEARCHER (through translator): I lost a lot of my family members. One day I would like to sit down and count and put a name to everyone. But when we start counting, it gives us vertigo.

AMANPOUR (voice-over): That emotional vertigo is the result of the mass slaughter we've been examining on this program, some call it the swiftest genocide in history. It took place over a mere 100 days back in 1994, when members of the Hutu majority wiped out up to 800,000 to a million members of the Tutsi minority as well as Hutu moderates, men, women and children, 20 percent of the country's population was slaughtered.

Dafroza Gauthier was born and raised in Rwanda, trained as a chemical engineer. But with her husband, Alain (ph), a French teacher who she met in her homeland almost 40 years ago, she's devoted her life to investigating the massacre of her people, one of the world's most heinous crimes. And bringing its perpetrators to justice. Vindication, like the mills of God, grind slowly. But this past February, a former captain in the Rwandan army was transported under heavy guard to a courtroom in Paris, the first such trial in French history. And after five weeks of testimony, in a landmark decision, he was sentenced to 25 years in prison.

For the Gauthiers, the verdict was validation that their lonely, often thankless work goes on, gathering evidence for new cases. They've exhausted their savings and at times their health. But they say it's only strengthened their marriage and their determination.

ALAIN GAUTHIER, RWANDAN GENOCIDE RESEARCHER (through translator): We don't feel hate towards those who have committed the genocide of the Tutsis, firstly because hate is useless and only hurts the one who feels it in his heart. And also because we believe in justice.

AMANPOUR (voice-over): Justice is possible, says Defroza. It wasn't an accident or a tsunami; no, people were killed in Rwanda by other Rwandans and they have to be judged.

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AMANPOUR: So the Gauthiers simply refuse to forget. And those who won't remember the past are doomed to repeat it, and they are repeating it now from Syria to Central Africa, the right to protection is a right yet to be won.

And that is it for our program tonight. Remember you can always contact us at our website, amanpour.com, and follow me on Twitter and Facebook. Thank you for watching and goodbye from London.